1. Field of the Invention
This invention relates to hydroxyacetonitrile disphosphonic acid and its salts, to a process for their production, and to their use as thresholders or as complexing agents.
2. Statement of Related Art
1-Amino-1,1-diphosphonic acids corresponding to the following general formula ##STR3## in which A, B and C represent aliphatic, cycloaliphatic or aromatic hydrocarbon radicals, in addition to which B and C can also represent a hydrogen atom, are known from the prior art. They are prepared by reaction of nitriles with phosphorus trihalides and subsequent hydrolysis or alcoholysis (German application 10 02 355), reaction of nitriles with phosphorous acid (German application 26 25 767) or reaction of carboxylic acid amides with phosphorus trihalides in the presence of phosphorous acid and subsequent hydrolysis (German application 19 58 123). Phosphonic acids corresponding to general formula (I) above have the ability to complex heavy metal ions and alkaline earth metal ions. Accordingly, they are widely used as complexing agents or chelating agents in the softening of water, in detergent manufacture, in the textile field and in papermaking.
It is known from German application 16 17 729 that 1-hydroxyethane-1,1-diphosphonic acid can be used as a complexing agent for inhibiting the formation of tartar.
U.S. Pat. No. 3,686,290 describes the synthesis of ethylene-1,1-diphosphonic acid and its use as a complexing agent for heavy metal ions.
In addition, structurally related compounds corresponding to the following general formula ##STR4## are known as complexing agents. In formula (II), B and C represent hydrogen or aliphatic or aromatic radicals in analogy to general formula (I) above, while D is a C.sub.1 -C.sub.5 alkylene radical. German application 34 34 667 and German patent 25 34 391 describe the use of compounds corresponding to general formula (II) and water-soluble salts thereof as complexing agents for alkaline earth metal ions, preferably calcium ions, and as thresholders. German patent 24 05 254 describes the use of the above compounds in the prophylaxis and treatment of disorders of the calcium or phosphate metabolism in the human and animal body.